Generally, the recording and reproducing apparatus is for recording and reproducing a video and/or an audio signal, in which a video tape recorder (VTR), an audio set, a digital audio tape recorder, a laser disk player, a camcorder, etc., can be exemplified. Among these, the hi-fi recording and reproducing apparatus which records and reproduces a video and an audio signal using a magnetic tape as a recording medium records first an audio signal and then a video signal on the same track during the recording procedure. Therefore, the audio signal is recorded on the substratum of the track and the video signal is recorded on the superstratum of the track, that is, on the upper portion with respect to that of the audio signal.
FIG. 1 is a block diagram of a prior art system for reproducing the video signal and audio signal, for example, the conventional VTR. First, in reproducing the video signal, video signal information which is recorded on a magnetic tape 10 is picked up by a video reproducing head 11a, and the output signal is amplified as a predetermined amplification factor in a pre-amplifier 12a. The amplified signal is demodulated through a video signal demodulator 14 and is output into a desired video signal.
Audio signal information recorded on magnetic tape 10 can be recorded by three methods, that is, using a pulse code modulation (PCM) signal method, an audio frequency modulation (AFM) signal method, or a linear modulation (LM) signal method. The PCM signal or the AFM signal is picked up through an audio reproducing head 11b and then is amplified by a predetermined amplification factor in a pre-amplifier 12b. The amplified signal passes through filters 13a and 13b, so that only those frequencies in a predetermined band are passed and the rest of the signal is attenuated. The signal output from filters 13a and 13b is input to a PCM demodulator 15, an envelope detector 16, and an AFM demodulator 17, respectively. Here, envelope detector 16 determines whether the signals output from filters 13a and 13b are PCM signals or AFM signals according to their respective frequency domains. In case of the PCM signal, an output selection circuit 19 is connected to PCM demodulator 15 so as to output the demodulated PCM signal as an audio signal. In case of the AFM signal, the output selection circuit 19 is connected to AFM demodulator 17 so as to output the demodulated AFM signal as the audio signal. However, as shown in a cross-sectional view of the magnetic tape of FIG. 2, since the PCM signal and the AFM signal are recorded on the substratum of the tape, when the audio signal is reproduced, the magnitude of the envelope is very small. Therefore, since the gain of envelope detector 16 should be considerably large, the design of the apparatus is difficult and the time constant has not been easily determined. Also, when the magnitude of the envelope is too small, even though its amplitude has been adjusted in envelope detector 16, the probability of error generation is high and error detection is slow.